The present invention relates to the fabrication of three-dimensional (3D) objects from computer-aided design (CAD) models using extrusion-based layered deposition systems. In particular, the present invention relates to generating build data for depositing roads of build material with extrusion-based layered deposition systems to form 3D objects.
An extrusion-based layered deposition system (e.g., fused deposition modeling systems developed by Stratasys, Inc., Eden Prairie, Minn.) is typically used to build a 3D object from a CAD model in a layer-by-layer fashion by extruding a flowable build material, such as a thermoplastic material. The build material is extruded through a nozzle carried by an extrusion head, and is deposited as a sequence of roads on a base in an x-y plane. The extruded build material fuses to previously deposited build material, and solidifies upon a drop in temperature. The position of the extrusion head relative to the base is then incremented along a z-axis (perpendicular to the x-y plane), and the process is then repeated to form a 3D object resembling the CAD model.
Movement of the extrusion head with respect to the base is performed under computer control, in accordance with build data from a host computer. The build data is obtained by initially slicing the CAD model of the 3D object into multiple horizontal layers (referred to herein as “sliced layers”). Then, for each sliced layer, the host computer generates a build path for depositing roads of build material to form the 3D object.
Each deposited road of build material has a road height along the z-axis. The road heights of the deposited roads are affected by a variety of factors, such as extrusion head speed, extrusion nozzle dimensions, and build material feed rates. These factors may be controlled such that the road heights are held constant, which is beneficial because the height of a given layer along the z-axis is based on the road heights of the deposited roads. Thus, when generating the build path for depositing roads of build material, a host computer may hold the road heights constant to ensure a substantially uniform layer thickness.
In addition to a road height, each deposited road of build material has a road width in the x-y plane, where the road width is proportional to the road height (e.g., about 20% greater than the road height). Because the road widths are proportional to the road heights, holding the road heights constant also holds the road widths constant as well. Based on these constant road widths, the host computer may generate the build path for depositing roads of build material based on a “road width resolution” that corresponds to the constant road widths. While relying on the given road width resolution, the host computer may properly offset each path so that the roads of build material are deposited adjacent each other without overlapping.
While relying on a constant road width resolution to generate a build path is beneficial for quickly generating build data and for rapid depositions of build material, it also presents an issue with small void regions that occur in the generated build path. Such void regions are typically smaller than the constant road width resolution, and therefore, are ignored during data generation. This may result in small cavities being formed between the deposited roads of build material, which correspondingly increases the porosity of the resulting 3D objects, thereby reducing the structural integrities and sealing properties of the resulting 3D objects. As such, there is a need for a method of generating build data that is effective for depositing roads of build material in small void regions.